Add F-Curve Modifier for multiple F-Curves at once?
With a script

These things are most easily done with a script.

The script below, looks for all pose bone fcurves, all posebone scale fcurves and all posebone quaternion fcurves and assigns them to variables pbfcurves, scalefcurves and rotfcurves respectively.  Note if you are using Euler rotation change to rotation_quaternion to rotation_euler

If you know the action is named "Snurfball" then uncomment and edit  #action = bpy.data.actions["Running"] to   

action = bpy.data.actions["Snurfball"]


Uncomment, (delete #) to remove all modifiers from all posebone fcurves

demod(pbfcurves)    


To add strength 2 noise to all scale fcurves

noise(scalefcurves, strength=2.0)


To add strength 2, depth 4 noise to all quaternions

noise(rotfcurves, strength=2, depth=4)


Make your edits, Select the rig object and run script.  A single CtrlZ generally does a good job undoing, but as always: please backup first.

import bpy

context = bpy.context
ob = context.object
action = ob.animation_data.action
#action = bpy.data.actions["Running"]

def demod(fcurves):
    fcs = fcurves[:]
    while fcs:
        fcurves.remove(fcs.pop())

def noise(fcurves, scale=1.0, strength=1, depth=0, phase=1.0, offset=0.0):
    for fc in fcurves:
        m = fc.modifiers.new(type='NOISE')
        m.scale = scale
        m.strength = strength
        m.depth = depth
        m.phase = phase
        m.offset = offset


pbfcurves = [fc for fc in action.fcurves if fc.data_path.startswith("pose.bones")]


scalefcurves = [fc for fc in pbfcurves if fc.data_path.endswith(".scale")]

rotfcurves = [fc for fc in pbfcurves if fc.data_path.endswith(".rotation_quaternion")]

# clean modifiers from all fcurves

#demod(pbfcurves)

# add noise to all scale fcurves

noise(scalefcurves, scale=0.4, strength=2.0, offset=-5)


Further to this if you are adventurous, can do this from the python console.  Here I've found all the fcurves with a datapath, converted to lower case that contains the word "arm"

&gt;&gt;&gt; action = D.actions['metarigAction']
&gt;&gt;&gt; armfcurves = [fc for fc in action.fcurves if fc.data_path.lower().find("arm") &gt; -1]
&gt;&gt;&gt; for fc in armfcurves:
...     fc.data_path, fc.array_index
...     
('pose.bones["upper_arm.L"].location', 0)
('pose.bones["upper_arm.L"].location', 1)
('pose.bones["upper_arm.L"].location', 2)
('pose.bones["upper_arm.L"].rotation_quaternion', 0)
('pose.bones["upper_arm.L"].rotation_quaternion', 1)
('pose.bones["upper_arm.L"].rotation_quaternion', 2)
('pose.bones["upper_arm.L"].rotation_quaternion', 3)
('pose.bones["upper_arm.L"].scale', 0)
('pose.bones["upper_arm.L"].scale', 1)
('pose.bones["upper_arm.L"].scale', 2)
('pose.bones["forearm.L"].location', 0)
('pose.bones["forearm.L"].location', 1)


All location.y arm fcurves

&gt;&gt;&gt; armfcurves = [fc for fc in action.fcurves if fc.data_path.lower().find("arm") &gt; -1 and fc.array_index == 1 and fc.data_path.endswith("location")]
&gt;&gt;&gt; for fc in armfcurves:
...     fc.data_path, fc.array_index
...     
('pose.bones["upper_arm.L"].location', 1)
('pose.bones["forearm.L"].location', 1)
('pose.bones["upper_arm.R"].location', 1)
('pose.bones["forearm.R"].location', 1)

&gt;&gt;&gt;